Role of the Autonomic Nervous System in the Hemodynamic Response to Hyperinsulinemia-Implications for Obesity and Insulin Resistance

The association between triglyceride-glucose index and related parameters and risk of cardiovascular disease in American adults under different glucose metabolic states

BACKGROUND

Cardiovascular disease (CVD) encompasses an array of cardiac and vascular disorders, posing a significant threat to global health. It remains unclear whether there exists an association between triglyceride-glucose index (TyG) and its derived indices and the incidence of cardiovascular disease, and in particular, the strength of the association in populations with different glucose metabolisms is not known.

METHODS

Data extracted from the National Health and Nutrition Examination Survey (NHANES) covering the period from 1999 to 2020, involving a cohort of 14,545 participants, were leveraged for the analysis. Statistical assessments were executed utilizing R software, employing multivariable logistic regression models to scrutinize the correlation between TyG and its associated parameters with the incidence of cardiovascular disease across diverse glucose metabolism categories. Interaction analyses and restricted cubic splines were applied to evaluate potential heterogeneity in associations and investigate the link between TyG and its derivatives with the occurrence of cardiovascular disease. Furthermore, receiver operating characteristic curves were constructed to evaluate the extent of variability in the predictive performance of TyG and its derived parameters for cardiovascular disease across distinct glucose metabolic statuses.

RESULTS

This study found that TyG and its related parameters were differentially associated with the occurrence of cardiovascular disease in different glucose metabolic states. Curvilinear correlations were found between TyG in the IFG population and TyG-WC, TyG-BMI, and TyG-WHtR in the impaired glucose tolerance (IGT) population with the occurrence of cardiovascular disease. In addition, the introduction of TyG and its derived parameters into the classical Framingham cardiovascular risk model improved the predictive performance in different glucose metabolism populations. Among them, the introduction of TyG-WHtR in the normal glucose tolerance (NGT), impaired fasting glucose (IFG), IFG & IGT and diabetes groups and TyG in the IGT group maximized the predictive power.

CONCLUSIONS

The findings provide new insights into the relationship between the TyG index and its derived parameters in different glucose metabolic states and the risk of cardiovascular disease, offering important reference value for future clinical practice and research. The study highlights the potential for improved risk stratification and prevention strategies based on TyG and its derived parameters.

Association of the triglyceride-glucose index variability with blood pressure and hypertension: a cohort study

BACKGROUND

Several studies have indicated that the triglyceride-glucose index (TyG) index is associated with hypertension; however, evidence on the association of change in the TyG index with blood pressure and hypertension is limited.

AIMS

To assess the association of the TyG index with blood pressure and hypertension.

DESIGN

A cohort study.

METHODS

We included 17 977 individuals with a mean age of 60.5 years from the Dongfeng-Tongji cohort. The TyG index was calculated as ln [fasting triglyceride (mg/dl)×fasting glucose (mg/dl)/2]. Hypertension was defined as blood pressure ≥140/90 mmHg, self-reported current use of antihypertensive medication or self-reported physician diagnosis of hypertension.

RESULTS

In the longitudinal analyses, we found a linear dose-response relationship between changes in the TyG index and change in blood pressure. Each one-unit change in the TyG index was associated with a 1.93 (1.23-2.63) mmHg increase in systolic blood pressure (SBP) and a 1.78 (1.42-2.16) mmHg increase in diastolic blood pressure (DBP). During a median follow-up of 9.37 years, a total of 3594 individuals were newly diagnosed with hypertension. We also found a linear dose-response relationship between the TyG index and the incidence of hypertension. The hazard ratio (HR) of hypertension for each one-unit increase in the TyG index was 1.21 (1.13-1.29). In addition, the best cut-off point of TyG for predicting hypertension was 8.4797, with sensitivity, and specificity of 57.85% and 55.40%, respectively.

CONCLUSIONS

The TyG index had a positive dose-response relationship with blood pressure and could be used to predict the risk of hypertension.

Primordial Drivers of Diabetes Heart Disease: Comprehensive Insights into Insulin Resistance

Insulin resistance has been regarded as a hallmark of diabetes heart disease (DHD). Numerous studies have shown that insulin resistance can affect blood circulation and myocardium, which indirectly cause cardiac hypertrophy and ventricular remodeling, participating in the pathogenesis of DHD. Meanwhile, hyperinsulinemia, hyperglycemia, and hyperlipidemia associated with insulin resistance can directly impair the metabolism and function of the heart. Targeting insulin resistance is a potential therapeutic strategy for the prevention of DHD. Currently, the role of insulin resistance in the pathogenic development of DHD is still under active research, as the pathological roles involved are complex and not yet fully understood, and the related therapeutic approaches are not well developed. In this review, we describe insulin resistance and add recent advances in the major pathological and physiological changes and underlying mechanisms by which insulin resistance leads to myocardial remodeling and dysfunction in the diabetic heart, including exosomal dysfunction, ferroptosis, and epigenetic factors. In addition, we discuss potential therapeutic approaches to improve insulin resistance and accelerate the development of cardiovascular protection drugs.

The Effect of Acute Hyperglycaemia Induced by Oral Glucose Load on Heart Rate Variability and Skin Microvascular Reactivity in Young Adults

We aimed to elucidate the effects of acute hyperglycaemia, induced by an oral glucose tolerance test (OGTT), on the autonomic nervous system (ANS) and skin microvascular reactivity at the time point of peak plasma glucose concentration (cglc) in 20 young, healthy participants. We assessed their heart rate variability (HRV) as a measure of the ANS activity and the parameters of post-occlusive reactive hyperaemia (PORH) to estimate skin microvascular reactivity as measured by laser Doppler (LD) fluxmetry. The tests were repeated 30 min after a standard OGTT (75 g glucose dissolved in 250 mL water) and, in a separate control experiment, after drinking the same amount of water. Participants had their cglc and serum insulin measured at three consecutive time-points according to the testing protocol. The low-frequency (LF) spectral power, the LF to high-frequency (LF/HF) ratio, and the diastolic blood pressure increased significantly more after water than after OGTT, and there was a trend of the peak LD flux of PORH decreasing more after OGTT than after water. Significant correlations between some PORH and all the HRV parameters and cglc increase after OGTT were found, implying diminished vascular reactivity evoked by hyperglycaemia in healthy subjects with lower glucose tolerance.

Effects of Medications on Heat Loss Capacity in Chronic Disease Patients: Health Implications Amidst Global Warming

Pharmacological agents used to treat or manage diseases can modify the level of heat strain experienced by chronically ill and elderly patients via different mechanistic pathways. Human thermoregulation is a crucial homeostatic process that maintains body temperature within a narrow range during heat stress through dry (i.e., increasing skin blood flow) and evaporative (i.e., sweating) heat loss, as well as active inhibition of thermogenesis, which is crucial to avoid overheating. Medications can independently and synergistically interact with aging and chronic disease to alter homeostatic responses to rising body temperature during heat stress. This review focuses on the physiologic changes, with specific emphasis on thermolytic processes, associated with medication use during heat stress. The review begins by providing readers with a background of the global chronic disease burden. Human thermoregulation and aging effects are then summarized to give an understanding of the unique physiologic changes faced by older adults. The effects of common chronic diseases on temperature regulation are outlined in the main sections. Physiologic impacts of common medications used to treat these diseases are reviewed in detail, with emphasis on the mechanisms by which these medications alter thermolysis during heat stress. The review concludes by providing perspectives on the need to understand the effects of medication use in hot environments, as well as a summary table of all clinical considerations and research needs of the medications included in this review. SIGNIFICANCE STATEMENT: Long-term medications modulate thermoregulatory function, resulting in excess physiological strain and predisposing patients to adverse health outcomes during prolonged exposures to extreme heat during rest and physical work (e.g., exercise). Understanding the medication-specific mechanisms of altered thermoregulation has importance in both clinical and research settings, paving the way for work toward refining current medication prescription recommendations and formulating mitigation strategies for adverse drug effects in the heat in chronically ill patients.

Sympathetic transduction to blood pressure during euglycemic-hyperinsulinemia in young healthy adults: role of burst amplitude

Insulin acts centrally to stimulate sympathetic vasoconstrictor outflow to skeletal muscle and peripherally to promote vasodilation. Given these divergent actions, the "net effect" of insulin on the transduction of muscle sympathetic nerve activity (MSNA) into vasoconstriction and thus, blood pressure (BP) remains unclear. We hypothesized that sympathetic transduction to BP would be attenuated during hyperinsulinemia compared with baseline. In 22 young healthy adults, MSNA (microneurography), and beat-to-beat BP (Finometer or arterial catheter) were continuously recorded, and signal-averaging was performed to quantify the mean arterial pressure (MAP) and total vascular conductance (TVC; Modelflow) responses following spontaneous bursts of MSNA at baseline and during a euglycemic-hyperinsulinemic clamp. Hyperinsulinemia significantly increased MSNA burst frequency and mean burst amplitude (baseline: 46 ± 6 au; insulin: 65 ± 16 au, P < 0.001) but did not alter MAP. The peak MAP (baseline: 3.2 ± 1.5 mmHg; insulin: 3.0 ± 1.9 mmHg, P = 0.67) and nadir TVC (P = 0.45) responses following all MSNA bursts were not different between conditions indicating preserved sympathetic transduction. However, when MSNA bursts were segregated into quartiles based on their amplitudes at baseline and compared with similar amplitude bursts during hyperinsulinemia, the peak MAP and TVC responses were blunted (e.g., largest burst quartile: MAP, baseline: Δ4.4 ± 1.7 mmHg; hyperinsulinemia: Δ3.0 ± 0.8 mmHg, P = 0.02). Notably, ∼15% of bursts during hyperinsulinemia exceeded the size of any burst at baseline, yet the MAP/TVC responses to these larger bursts (MAP, Δ4.9 ± 1.4 mmHg) did not differ from the largest baseline bursts (P = 0.47). These findings indicate that increases in MSNA burst amplitude contribute to the overall maintenance of sympathetic transduction during hyperinsulinemia.

Impact of sex and diet-induced weight loss on vascular insulin sensitivity in type 2 diabetes

Vascular insulin resistance, a major characteristic of obesity and type 2 diabetes (T2D), manifests with blunting of insulin-induced vasodilation. Although there is evidence that females are more whole body insulin sensitive than males in the healthy state, whether sex differences exist in vascular insulin sensitivity is unclear. Also uncertain is whether weight loss can reestablish vascular insulin sensitivity in T2D. The purpose of this investigation was to 1) establish if sex differences in vasodilatory responses to insulin exist in absence of disease, 2) determine whether female sex affords protection against the development of vascular insulin resistance with long-term overnutrition and obesity, and 3) examine if diet-induced weight loss can restore vascular insulin sensitivity in men and women with T2D. First, we show in healthy mice and humans that sex does not influence insulin-induced femoral artery dilation and insulin-stimulated leg blood flow, respectively. Second, we provide evidence that female mice are protected against impairments in insulin-induced dilation caused by overnutrition-induced obesity. Third, we show that men and women exhibit comparable levels of vascular insulin resistance when T2D develops but that diet-induced weight loss is effective at improving insulin-stimulated leg blood flow, particularly in women. Finally, we provide indirect evidence that these beneficial effects of weight loss may be mediated by a reduction in endothelin-1. In aggregate, the present data indicate that female sex confers protection against obesity-induced vascular insulin resistance and provide supportive evidence that, in women with T2D, vascular insulin resistance can be remediated with diet-induced weight loss.

New insights into mechanisms of endothelial insulin resistance in type 2 diabetes

Insulin resistance in the vasculature is a hallmark of type 2 diabetes (T2D), and blunting of insulin-induced vasodilation is its primary consequence. Individuals with T2D exhibit a marked impairment in insulin-induced dilation in resistance arteries across vascular beds. Importantly, reduced insulin-stimulated vasodilation and blood flow to skeletal muscle limits glucose uptake and contributes to impaired glucose control in T2D. The study of mechanisms responsible for the suppressed vasodilatory effects of insulin has been a growing topic of interest for not only its association with glucose control and extension to T2D but also its relationship with cardiovascular disease development and progression. In this mini-review, we integrate findings from recent studies by our group with the existing literature focused on the mechanisms underlying endothelial insulin resistance in T2D.